For those who are interested in building and testing the Win32 changes I'm doing for filename fixups, I just checked in a much better version. What I had before was mainly code to check things, not change things, and was placed *after* the main app instance was created with the args.
Moving the code up above the instance creation made things much happier.
It still has a major problem in that things are stripped to bare filenames with no path preceding them, so files need to be placed in the same location as inkscape.exe to be tested. However, it should get things working with all Unicode names (not just those in the current ANSI code page).
The other thing to check is in src/io/sys.cpp at line 129. To get things opening correctly, we can probably simplify the code now that we're using GTK+ 2.6 or later on Windows.
Change if ( PrintWin32::is_os_wide() ) to if ( false )
and that should finish fixing things (aside from the full-path issue, of course). If anyone can verify that the sys.cpp change keeps things working with different names (non-ASCII, non-Cp1252, etc) that would be very good to hear.